HUNTSVILLE, Texas (AP) — A 33-year-old man convicted of carjacking and fatally shooting a stockbroker will head to the Texas death chamber Wednesday, becoming the first person in the state executed with a single lethal drug.

Texas Department of Criminal Justice officials announced last week they were modifying a three-drug execution procedure used since 1982 because the state’s supply of one of the drugs — the muscle relaxant pancuronium bromide — has expired. Yokamon Hearn is to be executed using a single dose of the sedative pentobarbital.

Hearn was sentenced to death in the March 1998 slaying of Frank Meziere, 23. About 3½ hours before Hearn’s execution, set for Wednesday evening in Huntsville, the U.S. Supreme Court rejected appeals to halt it. None of the appeals addressed the change in the state’s execution drug policy.

Evidence shows that Meziere, of Plano, was cleaning his black convertible Mustang at a self-service car wash in Dallas when Hearn, then 19, and his friends approached. The men forced Meziere at gunpoint into his own car and drove him to an industrial area in a south Dallas neighborhood, where he was shot 10 times in the head.

Hearn, known to his friends as “Yogi,” already had a lengthy record that included burglary, robbery, assault, sexual assault and weapons possession.

In one appeal, Hearn’s lawyers argued that his mother drank alcohol when she was pregnant, stunting his neurological development and leaving him with mental impairments that disqualify him from execution under earlier Supreme Court rulings. Testing shows Hearn’s IQ is too high for him to be considered mentally impaired.

In another, his appeals lawyers claim the trial attorneys who handled his initial appeals failed to investigate his background and uncover evidence of his alleged mental impairment and troubled childhood.

Richard Burr, one of Hearn’s appeals lawyers, had acknowledged he had “a degree of hope, but still, it’ll be tough.”

State attorneys contested both appeals, arguing that information about Hearn’s background and upbringing had been “thoroughly investigated and addressed at trial” and that the evidence “does not substantiate any scenario other than that of Hearn’s guilt.”

Georgette Oden, an assistant Texas attorney general, argued Hearn’s latest appeal was improperly filed this week by circumventing lower courts and that it should have been filed years ago.

Hearn declined to speak with reporters in the weeks leading up to his scheduled punishment. In 2004, he avoided the death chamber when a federal court agreed his mental impairment claims should be reviewed and halted his execution less than an hour before its scheduled time.

Jason January, the former Dallas County assistant district attorney who prosecuted Hearn for capital murder, said to stop the punishment because of fetal alcohol syndrome “would be a free pass for anyone whose parents drank.”

“No question he had a tough background, but a lot of people have tough backgrounds and work their way out and don’t fill someone’s head with 10 bullets,” he said.

One of Hearn’s accomplices received life in prison. Two others got 10-year sentences.

Hearn will be the sixth Texas prisoner executed this year and the 483rd since 1982. At least eight other Texas prisoners have execution dates in the coming months, including three in August.